The present invention relates to air compressors, and, more particularly, to filters and air/oil separators.
Oil-lubricated, rotary compressors are commonly used in industry and elsewhere to reliably produce large quantities of pressurized air. However, in these types of air compressors, the air, as it is compressed and passes through the compressor, comes into direct contact with the oil or other liquid (e.g., synthetic lubricant from a nearby reservoir) used to cool and lubricate the compressor""s moving parts (e.g., a rotor with mounted vanes or a rotating screw). In doing so, an air/oil aerosol is formed, consisting of pressurized air interspersed with tiny particles or droplets of oil. To ensure that the pressurized air is relatively clean, as is required for most applications, the oil must be removed from the pressurized air prior to its being exhausted for use. Additionally, the separated oil can be channeled for re-use in the compressor.
In order to separate the oil or other lubricant from the pressurized air, most rotary vane or screw compressors are provided with an air/oil separator 20, as shown in FIG. 1 (labeled xe2x80x9cPrior Artxe2x80x9d). The air/oil separator 20 is a compound, cylindrical, coalescing element that separates the oil from the compressed air. The air/oil separator 20 is attached to the inside of a separator tank 22, and is positioned such that the interior of the separator is in fluid communication with the compressor""s air discharge or exhaust line 24. The compressed air/oil aerosol is routed into the separator tank 22 and through the air/oil separator 20, oftentimes after first passing through a baffle or other coarse separator that removes large particles of oil. The separator 20 is typically provided with an outer, tubular, coalescing separator 26, and an inner, concentric, tubular drain separator 28, the two being supported and/or separated by a concentric, tubular, perforated steel cylinder 30 (hereinafter referred to as the xe2x80x9ccagexe2x80x9d 30). Additionally, other filter or separator stages (not shown) may be provided. It should be appreciated that the separator 20 acts like a filter in the sense of removing oil from air. However, unlike a filter, where particles are trapped in the filter elements, the separator 20 coalesces oil, which then drains to the bottom of the separator 20.
The outer separator element 26 is typically composed of a fine fibrous separator media upon which the oil particles tend to coalesce. As oil particles build up, they move downwards, run together, and collect at the bottom end of the separator 20. The inner separator element 28 is typically composed of a coarser fibrous media, and is provided to facilitate oil drainage and to collect oil that gets re-suspended in the air flow downstream the outer filter 26. Oil that collects at the bottom of the separator 20 is collected for reuse via a scavenge line 32 extending into or through the tank 22.
As should be appreciated, in order for the separator 20 to strip the oil from the compressed air/oil aerosol, the aerosol must pass through the separators 26, 28. For this purpose, the bottom of the air/oil separator 20 is provided with an end cap 34. The end cap 34 blocks the bottom end of the separator""s central cavity 36, and seals the bottom ends of the separators 26, 28. Without the cap 34, the aerosol would follow the path of least resistance by traveling directly through the separator""s central cavity 36 and into the discharge line 24 without passing through the separators 26, 28.
Numerous methods have been used over the years to fasten the cap 34 to the bottom of the separator 20. Originally, as shown in FIG. 1, and as also shown in U.S. Pat. No. 6,093,231 to Read et al., the cap 34 was simply glued on via an epoxy 38 or the like. The epoxy, besides acting as a connector, also provided a seal between the cap 34 and the bottoms of the separators 26, 28. However, although this would work for a while, the cap 34 would still tend to fall off after a relatively short period of time. This is because the components in an air compressor, and especially the separator 20, are subject to a number of deleterious forces. For example, oil and other chemicals in the compressor tend to attack epoxy, especially if the compressor is left off for a while. Additionally, the separator 20 is subject to temperature changes during the compressor""s duty cycle, and there is always the possibility of mechanical shock. Finally, when a check valve, a safety valve, or some other component of the compressor upstream from the separator 20 opens or fails (which happens relatively frequently), the separator is subject to a transient but high magnitude pressure differential or backlash. More specifically, in normal operation the pressure on the outer side of the cap is greater than the pressure on its inner side, helping the cap to stay in place. When the pressure suddenly drops on the outer side, the high pressure remaining on the inner side can literally blow the cap 34 off the end of the separator 20.
In the case mentioned above, using epoxy by itself left the cap 34 especially vulnerable to all the aforementioned forces. If the oil did not cause the cap to fall off by gradually degrading the epoxy, temperature or pressure differentials would. Of course, when the cap 34 fell or blew off, the air/oil separator 20 would have to be replaced before the compressor could be used again. Additionally, with epoxy separating the cap 34 from the rest of the separator 20, the cap would not be electrically grounded, raising the possibility of static discharge and fire.
To supplement the epoxy seal/connection, mechanical connectors or fasteners have been used in the past to connect the cap to the rest of the separator. For example, according to one method (not shown), the cage 30 was made wider and/or provided with end flanges, and the cap was riveted to the end of the cage 30. Although this functioned better than only using epoxy, the rivets were still subject to failure via chemical attack, plus it was difficult to provide rivet connections, considering the limited space, that were strong enough to withstand significant or repeated pressure differentials.
According to another method (not shown), metal straps were welded between the separator""s flanged ring top 40 and the bottom of the cap. Such straps would typically not work very well because their weld connections would tend to fail subsequent periodic temperature fluctuations. Additionally, the straps would tend to bow axially inwards, preventing secondary components (other filter units, separators, etc.) from fitting into the separator""s inner cavity 36, and it was effectively impossible to install such straps using an automated machine.
Other methods included using a central threaded rod, similar to the apparatus shown in U.S. Pat. No. 5,207,811 to Buonpastore, to connect the cap 34 to a cross brace placed across the ring top 40; and, as shown in U.S. Pat. No. 5,605,555 to Patel et al., providing a gripping surface for the sealing epoxy via dimples or similar features in the end cap 34 and ring top 40. Regarding the former method, secondary components could not be installed in the central cavity 36, and, regarding the latter method, the interconnections were still reliant on the efficacy of the epoxy, plus there was no effective grounding connection between the cap and the rest of the metal parts of the separator.
A final prior art design (not shown) involved the use of an outer cage connected to the outer periphery of the ring top 40 and crimped or flanged over the bottom periphery of the cap 34. Here, the cap 34 would still blow off from pressure backlash, mainly because the peripheral flange or crimping would fail, it generally being difficult to provide a cage strong enough to withstand large pressure differentials yet malleable enough to easily flange or crimp.
Accordingly, it is a primary object of the present invention to provide an improved system for attaching an end cap and a ring top to an air/oil separator, wherein said end cap and ring top are highly resistant to becoming detached via chemical corrosion or temperature or pressure differentials within the operating range of the air compressor.
Another object of the present invention is to provide a cap attachment system for an air/oil separator wherein all the metal parts are electrically connected for proper grounding.
Yet another object of the present invention is to provide a cap attachment system for an air/oil separator wherein the cap attachment system also serves to reinforce and maintain the shape of a cylindrical separator cage.
Still another object of the present invention is to provide a cap attachment system for an air/oil separator wherein the cap is easily attachable and wherein the separator can be automatically assembled by a machine.
An improved cap attachment system is disclosed for securely attaching the primary metal components of an air/oil separator to one another. In the preferred embodiment, the system""s primary components comprise a plurality of unique metal clips and mating retainer strips. Other components (which existed previously) include a tubular, perforated metal cylinder, or xe2x80x9ccage;xe2x80x9d and two cap members, namely, a flanged ring top and an end cap.
Three of the retainer clips, spaced equidistant as around a circle, are connected to an inner side of the cap, as are three additional clips connected to an inner side of the ring top. Three of the retainer strips, bowed to have the same radius of curvature as the cage, are connected to an inner surface of the cage equidistantly along its bottom edge. Three more retainer strips are likewise connected to the inner surface of the cage along its top edge. The clips are positioned so that when the cage is brought to bear against the ring top and end cap, the clips engage the retainer strips. In this manner, the cage is attached at its top end to an underside of the ring top and depends therefrom, and is attached at its bottom end to the end cap.
Additionally, at some point prior to assembling the cage, end cap and ring top, a pleated, outer separator element is concentrically disposed about an outer periphery of the cage, and an inner separator element is concentrically positioned within the interior of the cage. Once the end cap and ring top are attached to the cage, the ends of the inner and outer separators lie within the confines of the ring top and end cap. The ends of the cage, the outer separator, and the inner separator are sealed against the ring top and end cap by an epoxy or the like disposed on the inner side of the end cap and ring top prior to or during assembly.